Ballast water is seawater stored in a ship to maintain balance of the ship. Typically, when a ship such as an oil tanker or a cargo ship leaves a port after finishing unloading of cargoes, it fills the left and right ballast tanks with seawater to balance the ship and prevent an event of drift, which is caused by locking of the propeller and buoyancy, to ensure safe voyage. After moving to another port, the ballast water is discharged from the ship in loading cargoes on the ship. However, if ballast water is discharged arbitrarily, it may disturb the marine ecosystem.
A ballast water treatment system refers to an apparatus or facility that removes harmful marine organisms and pathogens from ballast water, detoxifies the harmful marine organisms and pathogens or prevents introduction or discharge of the harmful marine organisms and pathogens in order to prevent the marine ecosystem from being destroyed or disturbed according to movement of ballast water.
There has been a need for prevention and minimization of a risk to the natural environment, human health, properties and resources raised by harmful aquatic organisms and pathogens. To meet the need, the International Maritime Organization adopted the International Convention for the Control and Management of Ship's Ballast Water and Sediments in 2004, obliging installation of a ballast water treatment system compulsory.
Techniques for the ballast water treatment system which have been developed and commercially available in the world are broadly classified into radiation of ultraviolet rays, electrolysis, and ozone injection. Regarding the technique of electrolysis, Korean Patent No. 1180334 discloses a system for parallel control of a ballast water treating apparatus using an electrolysis method. Regarding the technique of radiation of ultraviolet rays, Korean Patent No. 1567441 discloses a ballast water treatment apparatus. Regarding the technique of ozone injection, Korean Patent No. 1564244 discloses a hybrid ballast water treatment system having a pipe type water treatment unit and an ozone micro-bubbles unit.
The conventional ballast water treatment systems remove harmful marine organisms such as viruses from ballast water using radiation of ultraviolet rays, electrolysis or ozone injection, and then the ballast water is discharged to the sea or reused. However, since the ballast water contains not only viral microorganisms but also various other contamination sources which may contaminate or disturb the ecosystem, there is a demand for a water treatment system employing a combination of physical, chemical and physiological treatment techniques. Development of such water treatment system may also be applied to a fish farm treatment system for a fish farm such as a high-population pond farm in which water can be easily contaminated.